Turkish riot police have fired water cannons and tear gas at protesters in Istanbul's Gezi Park.

TURKISH police stormed an Istanbul park after protesters defied an ultimatum from Prime Minister Recep Tayyip Erdogan to end their occupation of the site, in a major escalation of more than two weeks of anti-government unrest.

Two hours after Erdogan warned of police intervention if protesters did not leave Gezi Park, the epicentre of nationwide protests, officers entered the green patch firing volleys of tear gas and jets of water.

Thousands of campers scrambled as police trampled tents, pulled down banners and broke down barricades in the park. A city cleaning crew then swiftly moved in to clear the site as darkness fell.

Earlier, police also used tear gas and bursts of water to disperse hundreds of demonstrators from Taksim Square, which borders Gezi Park.

The police action sent tensions soaring in the civil unrest in which four people have been killed and nearly 7,500 injured, and has posed the biggest challenge yet to the decade-long rule of Erdogan's Islamic-rooted government.

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Earlier, in a boisterous speech given before tens of thousands of flag-waving party faithful, Erdogan had threatened protesters that if they don't clear out Istanbul's Taksim Square, security forces "know how to clear it."

Supporters of Recep Tayyip Erdogan converged in Sincan, a suburb of the capital Ankara that is a stronghold of his Justice and Development Party. The rally came just hours after protesters camping out in the adjacent Gezi Park defied earlier warnings to leave, vowing to press on with a two-week sit-in that has galvanised demonstrations around the country.

Mr Erdogan warned protesters to cheers from the crowd: "I say this very clearly: either Taksim Square is cleared, or if it isn't cleared then the security forces of this country will know how to clear it."

A violent police crackdown on what began as an environmental protest over a redevelopment plan at the park has sparked a much broader expression of discontent about Mr Erdogan's government, and what many say is his increasingly authoritarian decision-making.

The anger has been fanned because riot police have at times used tear gas, water cannons and rubber bullets to disperse mostly peaceful protesters. Five people, including a police officer, have died and thousands of people have been injured, denting Mr Erdogan's international reputation.

Mr Erdogan, who was elected with 50 per cent of the vote for his third term in 2011, vehemently rejects the accusations by protesters and points to his strong support base.

A second pro-government rally is planned for Sunday in Istanbul, though Erdogan has previously said that the rallies were not designed as "an alternative" to the demonstrations at Gezi Park, but part of early campaigning for local elections next March.

On Saturday, Mr Erdogan lashed out at what he called the "plot" behind the biggest street protests in his 10-year tenure.

Protesters aid one another in the Divan Istanbul Hotel after riot police used tear gas to disperse the crowd near Gezi Park. Picture: Lam Yik Fei/Getty Images

"Over the last 17 days, I know that in all corners of Turkey, millions and billions have prayed for us," Mr Erdogan said, as he moved about the stage. "You saw the plot that was being carried out, the trap being set." He said his supporters represented the "silent masses."

"You are here, and you are spoiling the treacherous plot, the treacherous attack!" he said, insisting unspecified groups both inside and outside Turkey had conspired to mount the protests centered on Istanbul - and that he had the documents to prove it.

The crowd chanted in response: "Stand straight, don't bow, the people are with you!"

In his speech, he focused on some protesters who have clashed with polices - at time by throwing stones and firebombs.

"There is no breaking and burning here, we are people of love," Mr Erdogan said. "If people want to see the real Turkey, they should come here to Sincan."

Mr Erdogan already has offered to defer to a court ruling on the legality of the government's contested park redevelopment plan, and floated the possibility of a referendum on it. But concessions over the park seem to no longer be enough.

The Turkish protesters had been warned time and again but when the police intervention finally came today, it came suddenly, in a haze of acrid tear gas, confused screams and trampled tents.

"It's a reaction to the chemicals in the water cannon," the first aider explained.

Another injured man, gasping for air, was carried in by two volunteer medics.

A woman rushed to his aid with an inhaler.

At the nearby Hilton, the scene was similar, with hundreds milling around the reception desk as hotel guests looked on, unnerved.

Suddenly, around 20 riot police burst into the lobby, sparking an uproar.

"What the hell are you doing? You have no right to enter here," a guest bellowed.

The officers ignored him and tried to arrest a couple of demonstrators before hotel security personnel intervened.

The officers left, the sound of boos ringing in their ears.

In Gezi Park, police officers had established a security cordon.

A bulldozer was guided in to remove the burnt-out, graffiti-covered wreck of a car.

City cleaning crews in their green and yellow uniforms fanned out, ready to remove all trace of the protest that rocked the country.

"They took our goggles and gas masks," Mey Elbi, a yoga teacher, said as she clambered down the steps that lead out of the park. "I told them 'Please, I have asthma', but they didn't care."

"I won't give up," the 39-year-old vowed.

"We're angry, this is not over. The world has seen that together, we can stand up to Tayyip."

A stone's throw away, demonstrators clustered in narrow alleys, running to the action and away from it, challenging the police in tireless cat-and-mouse games.

In the main Istiqlal shopping street, hundreds braved the water cannon, greeting each salvo of water with bursts of applause, as the truck advanced slowly, but relentlessly, pushing the protesters further away from Gezi Park.

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